A heat source system provided with a plurality of heat source machines connected in parallel to each other is known (see, for example, PTL 1). In such a heat source system, generally, the operation of each of the heat source machines is performed so that the temperature of a heat medium delivered from a heat source machine side to an external load such as an air conditioner or a fan coil (hereinafter, referred to as a “heat medium delivery temperature”) is a set temperature (for example, 7° C.) which is set in accordance with the demand of an external load side.
In such a heat source system, in a case where a heat source machine which is not capable of exhibiting a rated capacity due to a reason such as degradation over time (hereinafter, referred to as a “capacity-degraded machine”) is included in operating heat source machines, there may be a concern of a water supply temperature greatly diverging from a set value.
Regarding such a problem, for example, PTL 1 discloses that a threshold is set with respect to a water supply temperature, and a forced increase stage is performed on a heat source machine in a stop state in a case of exceeding the threshold, to thereby prevent the water supply temperature from rising.
In addition, PTL 1 discloses that, in consideration of the possibility of a forced increase stage temperature set value for performing a forced increase stage on a heat source machine being lower than a normal decrease stage temperature set value, the decrease stage temperature set value is reset to a value obtained by subtracting a predetermined temperature from the forced increase stage temperature set value after the forced increase stage, to thereby prevent an increase/decrease stage of the heat source machine from being repeated.